text:
Is there a website that shows past flight tracks of a few days back?
I'm looking for a website, like Flight Radar, that can display the positions of aircraft going back a few days (i.e. not a live map)

If you just need a few days then FlightAware let’s you do that. I think it goes back 7 days for free. Past that you have to pay. That is for a particular flight. FR24 has a history feature that will play back the whole radar starting at a particular time. It plays back at 12x speed, though.
On FR24 you just open the main screen, move the map where you want it then click the clock icon on the right side. Enter the time and date you’re interested in. Note that it’s in UTC time, so you’ll have to convert your local time to UTC.

Then it will begin playing back. You can see the time and playback speed on a bar at the bottom of the screen.

Thanks - where is this feature on Flight Aware?

Just search for the flight number. It will bring up th most recent one.then there’s a link above the map that says “see flight schedule.” Tap on that then select the one you want

I should have mentioned that I don't know the flight number, but I do know where and when it flew overhead.

Then you can use the FR24 function to play back the radar at the time to find the flight num. I’ll edit some instructions into my answer


text:
Why do pilots have the ability to turn off the transponder in-flight?
These days, when reading news about missing Malaysia Airlines Boeing 777-200, I keep coming across a scenario where pilot might have deliberately turned off the transponder which is used for the communication of flight with ATC.
When there is a possibility that any bad thing can happen when pilot turn off transponder, why would one give the ability of turning off the transponder to a pilot when he/she usually depends on instructions from ATC or flight control. Is there anyway that ATC can turn on transponder back from ground?

This has been a question on my head since the day one the flight went missing. How odd we have advanced so much that we cannot perfect a simple transponder to be non faulty and need a manual breaker for just in case situations :(

The simple answer to your question is "pilots are trusted", we are after all in complete and authoritative control over the aircraft you are flying in.  If you didn't trust us with this authority, presumably you wouldn't board an airplane.

Actual transponder-related accidents have occurred before; it's just that the media attention this event has been getting is making people "freak out" about it (media has a tendency to make people suddenly upset about issues that aren't new). For example, the crash of Gol 1907 in 2006 was caused in part by an accidental deactivation of a transponder (the FAA later released a safety alert regarding accidental deactivation of EMB-135/140/145 transponders).

Transponders are a part of a decades old systems that works as designed. A possible "solution" would be something similar to LoJack/OnStar installed so it cannot be access from the inside of the plane. The trucking industry uses something like this as well. It could report "continuously" using independent GPS. And it could be on aircraft power with battery backup.

@casey: meh, I trust the pilot but I still don't mind minor displays of distrust by the ground authorities such as breathalyzing you ;-)

@SteveJessop if only it were minor.  I don't mind the "random" checks, but if a passenger even jokes he smells alcohol, just plan for a 3 hour departure delay while required actions to be tested play out.

@casey: right, from my personal POV there's breathalyzing you and then there's spending 3 hours running every test they have when I've got a connection to make. Presumably even if it was a good idea to control the transponder from outside the plane (i.e. all the technical reasons below magically went away), bureaucracy would find a way to make that a PITA for someone.

@SteveJessop no, thats just 3 hours for a breathalyzer.  Outstations are not usually equipped to perform even that test to DoT standards and have to bring specific people in, which takes time.

Basically everything that consumes power on an aircraft can potentially cause interference, short-circuits, or otherwise jeopardize the safety of flight and therefore must be switchable. Sometimes the switch is in the form a button, otherwise by a fuse.
There are several particular reasons that the transponder can be turned off.
If the transponder malfunctions, it may cause interruptions to all ATC surveillance in an area. There have been occurrences in the past that due to a fault the transponder it was basically acting as a radar jammer.
In one particular incident it took a while before the aircraft that caused it was identified and after requesting the pilot to switch of the transponder, secondary surveillance was restored.
Another reason is that when the aircraft is at the gate, the transponder is switched of to reduce the amount of radio transmissions. 100 aircraft on the surface of a large airport can produce a massive Radio Frequency noise, which negatively affect radar systems. When taxiing, radar replies are useful for aircraft identification, hence the transponder is switched on at push-back or engine start.

For an example to see how such requirements are worded in aircraft certification regulations, see rbp's answer.

The focus here and in the media1 on the transponder in relation to hijacks is a red herring. If an aircraft is hijacked, there are way more important things to worry about than an active radar transponder.
If hijackers turn off the transponder it means that they have access to the cockpit already.
1This answer was written shortly after flight MH370 went missing while en-route from Kuala Lumpur to Beijing. Initial speculation focussed on a possible hijack scenario.

It's also worth noting that if the transponder is switched off you generally only lose two pieces of information: the flight identification (mode A & mode S data) and altitude (mode C data). Primary radar will still paint a target (albeit unidentified) as long as the aircraft is within radar range.

@voretaq7 true, provided that you have primary radar available.

that's usually a good assumption since secondary transceivers are often colocated with primary dishes (there are a few places I'm aware of where there's no primary radar & only the transponder returns are plotted though - it may be more common outside the US since radar installations are rather expensive...).

The range of the primary is often limited. Long range primary consumes an awful lot of power and requires active cooling. Expensive gadget :-)

+1 "The focus here and in the media on the transponder in relation to hijacks is a red herring". Media focus on any thing in any event is frequently a red herring.

Shouldn't it be such that if the transponder is switched off, the ATC comes to know about it immediately?

@BobbyAlexander In general that is the case. If the aircraft is flying within the operational coverage area of a secondary radar, there will be an indication on the controller display when the secondary transponder stops replying. However, when the aircraft is just handed over to the adjacent control area or is flying out of the radar coverage, there is no indication since the aircraft's transponder is no longer a concern to the air traffic controller.

" If an aircraft is hijacked, there are way more important things to worry about than an active radar transponder."  Really?  If there was some way of clearly knowing the exact position of aircraft at all times (I'd prefer satellite), could one not only have a much better idea of where a crashed plane is, but have a better chance of intercepting 9/11 style attacks?

@NPSF3000 yes really. The transponder is not a magic bullet. It is for Air Traffic Control surveillance of cooperating aircraft. If you need to find a crash site you use an ELT (via satellite), if you need to intercept something that does not cooperate, you have the military track it using primary radar.

@DeltaLima - but as we can see in this instance (and possibly others such as 9/11) military radar is near useless - it does not cover everywhere (e.g. over water) and even where it is covered the military may not pay attention (e.g. mh370 crossing back over malaysia).  I do agree that transponders may not be the best option, but in the design decision to add the turn off capability they should have put together a fail safe IMO.

I was taught that when changing transponder codes, e.g. going from 1200 to 4589(sic), that the transponder should be placed in standby while changing the code.

@dbasnett indeed you should do that to prevent intermediate codes being transmitted, confusing the ATC processing system and/or the controller. For new transponders with digital control heads the change is usually instantaneous, so no intermediate codes can be sent. You are going to have a hard time changing to code 4589 though :-)

Hence the (sic) ;)

Everything including the flight recorder has a power switch or circuit breaker. Electrical devices occasionally malfunction, and you don't want a sparky transponder setting the plane on fire when you can just turn it off and use the other one.

are you saying that the flight recorder (the black box) can be switched off as well?

@MartinVegter Yes, as Paul says, everything has a circuit breaker and that can be used to deactivate it.

Given what we know now, would it be possible to simply build a large battery into the transponder housing?

@Jaydles - like the ones in the Dreamliners that caught fire? ;)

For safety purpoes, in order for an aircraft to be certified under 14 CFR 23, it must meet the following requirement:

§23.1357   Circuit protective devices.
(a) Protective devices, such as fuses or circuit breakers, must be
  installed in all electrical circuits other than—
(1) Main circuits of starter motors used during starting only; and
(2) Circuits in which no hazard is presented by their omission.
(b) A protective device for a circuit essential to flight safety may
  not be used to protect any other circuit.
(c) Each resettable circuit protective device (“trip free” device in
  which the tripping mechanism cannot be overridden by the operating
  control) must be designed so that—
(1) A manual operation is required to restore service after tripping;
  and
(2) If an overload or circuit fault exists, the device will open the
  circuit regardless of the position of the operating control.
(d) If the ability to reset a circuit breaker or replace a fuse is
  essential to safety in flight, that circuit breaker or fuse must be so
  located and identified that it can be readily reset or replaced in
  flight.
(e) For fuses identified as replaceable in flight—
(1) There must be one spare of each rating or 50 percent spare fuses
  of each rating, whichever is greater; and
(2) The spare fuse(s) must be readily accessible to any required
  pilot.

For aircraft certified under 14 CFR 25, there is similar wording:

§ 25.1357 Circuit protective devices.
(a) Automatic protective devices
  must be used to minimize distress to the electrical system and hazard
  to the airplane in the event of wiring faults or serious malfunction
  of the system or connected equipment.
(b) The protective and control devices in the generating system must
  be designed to de-energize and disconnect faulty power sources and
  power transmission equipment from their associated busses with
  sufficient rapidity to provide protection from hazardous over-voltage
  and other malfunctioning.
(c) Each resettable circuit protective device must be designed so
  that, when an overload or circuit fault exists, it will open the
  circuit irrespective of the position of the operating control.
(d) If the ability to reset a circuit breaker or replace a fuse is
  essential to safety in flight, that circuit breaker or fuse must be
  located and identified so that it can be readily reset or replaced in
  flight.
(e) Each circuit for essential loads must have individual circuit
  protection. However, individual protection for each circuit in an
  essential load system (such as each position light circuit in a
  system) is not required.
(f) If fuses are used, there must be spare fuses for use in flight
  equal to at least 50 percent of the number of fuses of each rating
  required for complete circuit protection.
(g) Automatic reset circuit breakers may be used as integral
  protectors for electrical equipment (such as thermal cut-outs) if
  there is circuit protection to protect the cable to the equipment.

source: Stack Exchange

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sort: votes


text:
Have there been any studies on which fly-by-wire pilot interface is preferred; rate control or direct control?
Provided an aircraft with a fly-by-wire system, there are basically two possible choices when it comes deciding how to let the pilots interface with it:

rate control / attitude hold: a deflection of the stick will command a certain rate, releasing it will make the system maintain the current attitude. See the Airbus Normal control law.
direct control: a deflection of the yoke will directly translate to a deflection of the surfaces, mimicking the "old" mechanical control setup. It is my understanding that this is the design choice of Boeing in its new aircrafts.

I do not wish to discuss how Airbus and Boeing made their design decisions, but rather see if there has been performed a study on what interface is preferred by pilots, eventually differentiating among private/commercial pilots or Airbus/Boeing certified pilots or even pure civil/(former) military pilots.
Does any of you have any reference?

I predict that most pilots will prefer whichever style they're most used to.

A good place to start is this text "Human Factors in Aviation" http://amzn.com/0123745187. If I recall, there was a chapter in there on ergonomics with some studies cited.

@Canuk, I had a look through the references and the chapters, but to me it seems more focused on the physical aspects (levers/buttons/instruments locations and such) rather than the fly-by-wire "handling qualities" (if you allow this terminology)

@Federico, I had the wrong book, "Human Factors in Flight" (http://amzn.com/1857421353) is what I was thinking. There is a chapter on "Displays and Controls" and while the text is admittedly dated, it offers this unattributed sentence about the Airbus "...these features...have proved quite controversial, it must be admitted that most pilots who fly these aircraft, like them very much." (p.264)  I think it might be hard to find an actual study since it sounds like what you're after is a subjective opinion, however, perhaps a study exists from an ergonomic or human-factors related perspective.

related discussion. It is not as simple as choice #1 or choice #2. on the pitch axe, C* blend rate control and load factor. Consider also the difficulty of enhanced stability

I have no study to refer to, but I expect the results to differ very much from group to group.
For airline operations, I imagine the objective of the pilot is often to maintain a constant attitude, varied with a smooth transition to another attitude. This would be easy to achieve with the first option you describe.
For military operations, I think a rapid feedback is desired. This aligns better with the seconds option you describe.
When you would perform a study under pilots, the response you'll get will very likely be that they prefer whatever they are used to at the moment.

The second option does not provide any faster feedback. In fact, shortest reaction times are achieved by aerodynamically unstable designs, but for those, only the first option is actually usable.

Yes there have been, but quite some time ago so they may be hard to find in our present day Google world. Studies about the pilot-in-the-loop, who controls the aircraft by interpreting and reacting to the change in the outside world as function of their inputs. But these studies concentrated upon what configuration yields the most rapid and accurate result, and not on what the preference is. I was participant in the graduation project of one of my fellow university students in 1988: using a spring loaded side stick, place a representation of a satellite robot arm into a receptor bay, with different controller configurations. Stick displacement or applied stick force = robot arm rate, or robot arm position.
Force is often overlooked in these discussions, despite it providing an immediate feedback without having to look at where your hand is. We don't have direct position sensors in our hands! Rate feedback is an issue when you want to control a position: the extra integration that your brain needs to perform causes a time delay and estimation errors. Depending on the frequency response of the signals of course, the satellite end effector was very slow and it was very tedious to do anything with it using rate feedback.
We seem to control best when we are presented with an environment that replicates the forces of physics that we are built for. The F16 uses force feedback: the original stick did not move, input was how hard the pilot pulled on it. Then they started coming back with bent side sticks from Really Pulling Hard to out-turn the other guy, and the sticks became moveable, loaded by a stiff spring, but giving an extra force cue when the end of stick deflection was reached. I bet that General Dynamics did not design this control system with the preference of the generic pilot in mind though.
Boeings design choice is the one with the least amount of possible discussion risk: pilots have learned to integrate aircraft rate feedback (from their sensory organs), and have learned certain responses in order to control the aircraft. Airbus seems to be more inclined to incorporate recent research. Like you say, both make excellent aircraft with an excellent safety reputation and dissing one or the other would be a bit childish, really.

I asked about the signal, not the feedback. Airbus has no feedback, for example.

And feedback of environmental information is not what happens in the task of controlling an aeroplane?

Your last paragraph earns this answer +1, and more plusses were I allowed.

Thanks @KorvinStarmast. For experts like yourself there is no issue with how aircraft behave, you guys get right on top of anything. But there are 1,400 new airliners delivered every year, each requiring between 4 and 8 flight crews. Up to 20,000 new pilots per year, and a good portion of those are brand new pilots. Research into how zero-hour pilots carry out a pilot-in-the-loop task is very beneficial.

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text:
How is the actual ground speed of an airliner measured?
Do pilots have the "ground speed" information available?
If so, how is the ground speed measured? Or do they rely on GPS info to calculate it?

There are generally two ways of determining the ground speed from within the aircraft.
The first is by using an inertial navigation system. This consists of a number of accelerometers and gyroscopes that measure all accelerations and rotations of the aircraft throughout a flight. By mathematically integrating all measurements this navigation system is able to compute the speed and position of the aircraft at any time. The accuracy will degrade over time but ground speed is usually not far off, otherwise position would be far off very soon.
The second method uses external radio signals. Nowadays this is mostly GPS, but ground speed is also determined by using a number of VOR (VHF Omnidirection Range) and/or DME (Distance Measuring Equipment) stations. These navigation beacons are widely available over most continents. A navigation computer would select the right set of beacons and by analysing the rate of change of the beacon bearings / distances the aircraft's speed can be determined.
Modern navigation systems combine all these methods into a one solution. GPS, inertial navigation and DME measurements are then fused mathematically together to obtain a highly accurate and robust position and ground speed.

Ground speed and ground track are available and are determined by GPS.  Comparing two GPS derived locations will yield a velocity vector and ground speed is its magnitude.  This is also how winds are derived -- the difference between airspeed and heading compared to groundspeed and ground track.
Note that availability varies by airplane and installed equipment.  Any modern airliner will have this info on a primary or secondary display.  Smaller general aviation aircraft with an technologically advanced cockpit will have this info as well.  Smaller general aviation planes with just a GPS unit will have access to the information but it may not be convenient to reference. Those without even GPS will only be able to derive groundspeed from airspeed and reported winds with a flight computer manually.

Don't discard the good old VOR cross bearing every now and then. If you don't need the actual ground speed at this moment, but rather over the last 10 or 20 minutes, this old technique works well. Helped me once in a low-fuel situation to keep my co-pilot from panicking ;-)

A simple definition is:

Ground speed can be determined by the vector sum of the aircraft's
  true airspeed and the current wind speed and direction; a headwind
  subtracts from the ground speed, while a tailwind adds to it. Winds at
  other angles to the heading will have components of either headwind or
  tailwind as well as a crosswind component.

The issue with using GPS to determine airspeed is that a GPS does not know what the winds are. Although, weather forecast data can provide approximate wind velocity (direction and speed), it is not precise enough for situations where a few knots makes the difference between life and death.

Except, as you say, you don't know what the wind speed is so this method can't be used to calculate ground speed.

Would ground speed be an issue of life and death.
GPS can provide the time taken to traverse to path between two points, and if taken in the smallest possible distance with an appreciable amount of +- accuracy quantification for equipment capability does this not provide airspeed?
And wind can be calculated simply as Wind Speed = Airspeed - Groundspeed.
Distance over the ground measurable against charts or known courses, or again using GPS and its data and maps.

Some aircraft do have sensors that measure wind speed on them, and thus could use this method to determine ground speed


text:
Declaring an emergency: How should you report fuel remaining?
When a flight has to declare an emergency, they are asked for souls on board and fuel remaining. Sometimes the ATC will want fuel in minutes (or hours) and sometimes in pounds.
Could we get a description of why there is no standard for the fuel remaining description? In other words, why sometimes time remaining and other times weight?
(NOTE: I've tagged this FAA-regulations, because I mostly listen to RealATC, or variants, of US ATC, but this question shouldn't be limited to FAA Regs)

Good to read : Why is the total count of people on a plane given as the number of 'souls' on board?

There is no standard because there's no standard emergency. The response to "Say fuel onboard" (or the way the question is phrased) depends on who cares most about the answer.

Fuel Remaining (in minutes)
This is how you report it when you declare a minimum fuel emergency, and it's most useful for approach and tower controllers to know exactly how long they have to get you on the ground before your engine gets quiet (and if they can get you to an airport in that timeframe).
Fuel Remaining (in hours)
This is what you'll give for most general emergencies, and also what's entered on flight plans. It's the most generally useful number to a pilot or controller.
If you're VFR-only pilot stuck on top of an overcast and call ATC with a pan (urgency) message because can't see a way through the controller will want to know how far they can vector you to find a hole before it becomes a fuel emergency too.
Fuel Onboard (in Pounds/Kilograms or Gallons/Liters)
The folks who care about this number drive around in ugly fire trucks wearing silver jumpsuits (the ARFF crews): If the worst happens they want to know how big a fire they might have to deal with, and how much foam they're going to need to handle it.

"drive around in ugly fire trucks" Your airport needs to upgrade to one of these then.

@RonBeyer Yeah… ours are ugly

@RonBeyer link is dead. Here is a live one: https://commons.wikimedia.org/wiki/File:JMSDF_Rosenbauer_Panther_6x6(41-4126)_left_front_view_at_Maizuru_Air_Station_July_26,_2015.jpg

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text:
Is it legal to use a home-made Airband radio receiver in the United States?
I work at a local small airport (very small, if we get more than about 10 or 15 airplanes taking off/landing it's a "busy day") and I mow the runways (we have multiple grass ones).
Because of the visual obstructions of the tractor's cabin that I use I have to be even more careful than normal to check for in-coming planes and so I started looking into getting an air band radio for the tractor. However, they can be fairly expensive - not something I'd invest in unless I absolutely had to - and so I started looking into making my own.
I'd figured this was possible because I'd occasionally picked up communications on a cheap radio I had around my house (I live quite close to the airport, about a 5 minute bike ride). So, I went searching, and sure enough - this is a thing that is possible and has been done.
I found this post on Electrical Engineering.SE, Modify an AM/FM radio to an airband receiver, describing basically what could be done; and then this video done by MAKE, Weekend Project: Aircraft Band Receiver, showing it actually being done to cheap transistor radio.
Now, what I'm wondering is, is this a legal thing to do - or does the FAA have regulations on this sort of thing?

The relevant regulations would be FCC, not FAA, no?

@cpast Possibly. Or both. That's kinda why I came here :D

Although it is being used for aeronautical purposes, this question doesn't really belong here . . . The FAA does not control airspace under 100 feet AGL, and as long as you stay off nav aid and tower frequencies there probably is no regulation. Double check, though.

In other words, making your own radio receiver is not the issue, transmission is the issue.

@NoviceInDisguise So, so long as I don't transmit on any of those frequencies with my device, there's nothing wrong with listening in on radio traffic with my device?

I wouldn't think so, I can't imagine how they could possibly regulate it. Again, to be absolutely certain, you would have to some tremendously intense and specific research, but I think there would not be an issue with it.

@NoviceInDisguise Cool! Thanks for the help. I wasn't afraid there would be, but I figured I'd ask just the same, seeing as there is an SE community with people who're involved in aviation far more than I am.

@NoviceInDisguise: I agree that it's not practically controllable, but in some countries listening to broadcast that is not intended for public (which includes aviation bands) is indeed formally illegal.

Why are aviation frequencies not to be listened to?

@NoviceInDisguise Apparently, in the UK, it's illegal: http://www.liveatc.net/faq/

Interesting! However, the OP asked about the FAA, and since the US doesn't seem to have such a law . . .

It's surprising this isn't regulated. I'm not sure it's even wise. Consider if, at some point in the day, for some reason, your radio stops working. I don't want to cast doubt on your EE prowess, but your homemade radio would not be FAA certified, so this certainly seems like a plausible scenario. It's not clear that you would notice your radio had stopped working, and you might have a false sense of security and thus not be looking for incoming aircraft quite as diligently. This seems like a dangerous scenario, right?

There is no restriction to monitoring airband frequencies in the U.S., so you shouldn't have to worry about FCC rules as long as you aren't transmitting. Where you could run into trouble, though, is with the FAA. I'm not sure about this particular use case, which is why I'm not posting an answer, but the FAA is generally pretty strict about using unapproved equipment for aviation operational safety purposes. Someone that knows the relevant FARs (if any) might be able to provide an answer here.

Shouldn't your employer be providing you with appropriate safety equipment, rather than leaving you to jury-rig your own?

@DavidRicherby He said he thought about it, but because of how rarely we have any traffic at all, he deemed it not worth the expense. We rarely have any traffic when I'm mowing.

I think Canada got the law right on this issue.  In general, for all radio transmissions (including old cell phone frequencies) if it is broadcast, it is legal to listen to it.  However, for certain specific transmissions it is illegal to tell anyone else what one heard.  I.e. you can be nosy, but don't gossip.

FYI, the runway is supposed to be closed XXX with NOTAM when it is mowed.
There is no FAA or FCC limit on constructing homemade airband receivers in the United States.
You can also construct transceivers. As long as you do not sell a transmitter you are allowed to make and operate up to 5 of them.
The exemptions covering low power transmitters are covered in Part 15 of Title 47 in FCC regulations.
The maximum unlicensed radiated output power for airband is 500 μV/m @ 3 m. Typical commercial airband handheld transmitters go up to about 1 Watt and base stations up to 50 Watts. For your purposes a 1 Watt transceiver would probably be reasonable.
Note that typical receiver/scanner designs have an oscillator in their mixer that can generate a small amount of RF noise. Normally the signal is so weak it is completely undetectable. Nevertheless, there are specialized receivers that have no oscillator that some people use to listen to airband with zero chance of interference.

That's transmitters; the question was about receivers. And Part 15 prohibits intentional radiation in much of the aviation frequency bands, and has 150 uV/m for much of the airband (88-216 MHz are 150 uV/m, per 47 CFR 15.209(a)).

@cpast I updated the answer to cover receivers. The 150 limit is for constant transmission. Periodic transmissions (the normal case) have a limit of 500 as I wrote.

@TylerDurden Thanks for the answer!

While a receiver is good to keep you informed, if you ever need to warn away an aircraft, you'd need a transmitter, making the tractor a "ground station" requiring a license, and you personally would also need to be licensed to use it. As an employee of the airport, you might be covered by the airport's license to operate on its UNICOM frequency; I'd check with the airport's governing committee on this. In fact I'd question the airport manager's decision that it's not worth the expense; what's his liability for obstructing an active runway resulting in a collision?

@KeithS I don't think you need a license to transmit on airband. I do it all the time with hand helds. Gliders, balloon guys, hang gliders, all use airband radio transmitters with no license.

Because those guys are operating aircraft; a radio mounted or carried in an aircraft is "licensed by rule" and doesn't require a special station or operator's license (which also technically means your use of the radio should only be in furtherance of your responsibilities as a pilot). Radios installed in anything that doesn't leave the ground are "ground stations" under FAA/FCC regs and require a license to operate in airband. However I think a HAM license is sufficient for this purpose so long as you're not endangering operations by being an asshat on a nearby tower frequency.

@KeithS I am not talking about the pilots I am talking about the ground crews for those operations. There is, I believe, a general exception that allows anyone to transmit on certain frequencies, including airband, as long as the wattage does not exceed a certain amount. Most FBOs have transceivers and I guarantee you that none of them have "ham" licenses.

Also, FCC enforcement is pretty much zero as long as you're not interfering with licensed users. And no sane pilot is going to complain about warnings from a mowing crew.

If you want to listen only, you can airband scanners for ~$120USD. (wall-powered)
If you need to transmit or be portable, it's closer to $200.
https://www.sportys.com/pilotshop/avionics-and-radios/aviation-radios.html?dir=asc&order=position


text:
Do Gulfstream G650 rivets "smoke"?
Any G650 operators seeing "smoking" (i.e. they leave a dark trail on the fuselage) rivets on the fuselage at various locations?

Welcome to the site @Dak2Boe. Unfortunately your question isn't very clear, what are smoking rivets and why do you think they are being seen? Is it a news article, or another source?

Do you have any photos or specific locations on the A/C where this happens?

All rivets that are properly set will eventually "smoke" given a structure subjected to vibration that has been under-engineered, meaning not enough rivets per inch. The other cause would be improperly installed rivets. What looks like smoke is aluminum oxide produced by the movement of the surface, and the rivet rubbing a bit of it and sloughing it out and back along the airstream direction.

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text:
Did the FAA order the installation of "Cooper vanes?"
On November 24, 1971, a man hijacked a Boeing 727 and parachuted away, never to be found.
According to Wikipedia, this prompted (together with 2 other hijackings) the installation of "Cooper vanes" devices that prevented the opening of the 727 ventral airstair in flight.

In the United States, following three hijackings in 1972, the Federal Aviation Administration ordered that Boeing 727 aircraft be fitted with Cooper vanes.

Wikipedia cites "Beyond Fear: Thinking Sensibly About Security in an Uncertain World," which I don't have access to. I can find the same claim here and here.
I couldn't find any Federal Aviation Regulations specifically mentioning "727." I also couldn't find any Airworthiness Directives specifically mentioning "727" relevant to the situation. There is this one. Furthermore, the policy change isn't mentioned here.

Did the FAA order the installation of "Cooper vanes" on Boeing 727 aircraft?
Was the "order" in 1972?

I am asking this question because of a recent April 2 answer on Aviation.SE:

Boeing did have a small regional jet called the Boeing 727. This plane was designed to operate at smaller airports, with independence from ground facilities as a selling feature. The best example is that the 727 had built-in stairs in the rear underbelly of the aircraft. This could be opened in flight until some hijacker known as DB Cooper jumped out to make his escape.

Apologies if the background research is poorly conducted and irrelevant. I am not familiar with the best way to research historic and current FAA "orders."

This question has been asked on Skeptics.SE and wasn't well received.

Don't think anybody (source of bottom quote) who characterizes the 727 as a "small regional jet" has much credibility, or much clue.

FWIW, Beyond Fear (I have a copy) provides no citation for that claim.

@StephenS Thank you for your comment. This clears up a potential avenue of time-wasting.

@RalphJ The quote came from a question titled "Why didn't Boeing produce its own regional jet?" (cited in the question above). All answers (and all upvoted) included the Boeing 727 in the list of Boeing regional jets. If you disagree with this classification, you should post a separate (and better) answer.

As said in Skeptics about hijack->vane " The model of choice was the Boeing 727 — introduced in 1964 — because its rear air stairway was easier to open and exit during flight.
“There was a little fin on the back of the airplane,” said Crooks, who compared the 727’s rear stairway to the exit in a C-130. “When it got into the air stream there was a latch over this fin that held the door up. You could engage the hydraulic system and push it right through that fin. The fin would break right off.”" (from https://aviaed.wordpress.com/2011/11/23/d-b-cooper-case-inspired-copycat-hijackings-in-reno/)

The answer to both of your questions is "yes". The FAA ordered, in effect, the installation of "Cooper Vanes" and did do so in 1972.
The reason you could not find the answer may have been that the modifications were not called "Cooper Vanes" by the FAA and nor was the FAA targeting the 727 specifically. Instead they addressed ventral and tailcone exits on any aircraft.
CFR 14, Part 25 (Airworthiness Standards: Transport Category Airplanes), Subpart D (Design and Construction, Emergency Provisions) contains, since 31st of December 1972, the following text (emphasis mine):

Sec. 25.809
Emergency exit arrangement.
...
(j) When required by the operating rules for any large passenger-carrying turbojet powered airplane, each ventral exit and tailcone exit must be--
(1) Designed and constructed so that it cannot be opened during flight; and
(2) Marked with a placard readable from a distance of 30 inches and installed at a conspicuous location near the means of opening the exit, stating that the exit has been designed and constructed so that it cannot be opened during flight

This rule was announced in the Notice of Proposed Rulemaking. Notice No. 72-15, Issued on June 6th, 1972.
It clearly references the hijackings as the reason for this change.

....
In spite of concerted efforts made by the FAA and the air carriers,
  incidents continue to occur wherein the safety of the flight of
  aircraft engaged in passenger-carrying operations under Part 121 of
  the Federal Aviation Regulations has been jeopardized by persons
  intending to harm the crew or take command of the airplane. On a
  number of occasions in recent hijackings, the ventral exit of an
  airplane has been opened and a hijacker aboard has parachuted from the
  airplane through that exit. The agency recognizes that every possible
  step must be taken to deter persons from boarding aircraft for such a
  hijacking purpose. Accordingly, the FAA deems it appropriate to
  propose certain amendments to Parts 25 and 121.
Specifically, it is proposed to amend Sec 25.809 to provide that, when
  required by the operating rules, for any large passenger carrying
  turbojet powered air-plane an approved means must be provided so that:
(1) takeoff cannot be started if either the ventral exit or tail cone
  exit is not locked; and
(2) neither the ventral exit nor the tail cone
  exit can be opened in flight.
A similar amendment is proposed to be made to Sec 121.310, to become
  effective with respect to persons conducting operations under Part 121
  six months following its adoption.
However, it is to be noted that to achieve compliance with the
  proposed regulation both the ventral exit and tail cone exit would
  have to continue to meet all of the requirements applicable to their
  approval as emergency exits. Specifically, to achieve compliance, the
  conditions that would have to be met to obtain approval of
  modification to the locking mechanisms of these two exits are as
  follows:
(1) The mechanism must be locked while the airplane is
  aloft;
(2) Takeoff of the airplane cannot be started if either ventral
  or tail cone is not locked; and
(3) The exit must be available for use
  in the event of an emergency.

Since Part 25 is for airworthiness certification of new aircraft, an additional change was proposed to Part 121 so that operator of existing aircraft were given 6 months to apply the new rules to already certified aircraft.
Somehow the change to Sec 121.310 cannot be found in the FAA Regulatory and Guidance Library (at least not dated 1972), even though the final rule of 30th November 1972  includes it.
A revision of 121.310 from 1997 includes the text.

Special thanks to the FAA for making the pre-internet era rulemaking archives easily accessible through the internet.

I have accepted this answer. Could I ask how you went about finding it (e.g. tips)? This would be really helpful in the future.

Hello Barry, welcome to Aviation.stackexchange.com. Finding the rules and notices of rulemaking was harder than I thought. Experience with aviation regulations helped a lot. I knew that in regulations, rarely a solution (e.g. Cooper vane or more technical term) is mandated, but instead the desired effect is mandated. I also knew that to address already existing type certified aircraft, the FAA would have to address both the certification rule (e.g. Part 25) and the operational rules (e.g. Part 121). I also suspected that the problem would be address generically, not only on the Boeing 727.

Thanks for the detailed reply! You mentioned 2 very interesting points.  I suppose what you mean is experience helped you find the regulations?

I started my search in the FAA RGL on the history of part 121, as that would be the obvious choice to address existing airline operations. I couldn't find any relevant changes in 1972. In found relevant text in Part 125, Appendix A.1 (existing since 1978, so too new). Using words from that text, I found the relevant amendment to Section 25.809, which in turn linked to the proposed rulemaking and the final note.

Ah, thank you so much! I don't think I would've been able to do this, even after hours of searching.

You're welcome. As I said, experience with these kind of regulations / being an aviation nerd helped a lot :-)


text:
What is maximum displacement for aircraft engine?
Is there any standards or at least typical values of aircraft engine displacement and rotation relatively to the wing in flight? Actually I'm looking for that values at Boeing 747-400 RF or ERF.

There is no standard.  Even for a single plane and a single engine, there will be literally hundreds of different possible displacements depending on the condition. The engine manufacturer will split these into several categories.
First would be static versus dynamic loads. Static loads are the loads (or displacements) caused by gravity, thrust load, maneuvers or wind.  Dynamic loads are transient events caused by rotor unbalance, bird impacts, blade loss, etc.
The second category is the severity of the load.  There are several levels here.  First is a fatigue load.  The engine will experience this level of load (or displacement) on virtually every flight.  Therefore, all parts must be able to withstand this load and not have a fatigue failure.  The second level is a "limit" load.  This would be experienced by the engine say once every 4000 or 5000 flights.  E.g. a very rapid maneuver or a particularly hard landing. For this level, fatigue is not a concern, because the engine won't experience it very often.  Just have to make sure no parts yield.  Final level is "ultimate" load.  This is the highest load that will ever be experienced by any engine in the lifetime of the entire fleet (e.g. a fan blade out condition).  Yielding may be allowed here, as long as nothing breaks.
Depending on what you are looking for, the answers could vary between 0.001 inch and several inches. I'm not sure that you will be able to find exact values, as the airframer and engine manufacturers will regard this as proprietary information.

Consider you've designed an engine mount so that it is strong enough being as light as possible... but the engine moves 30 inches down and rotates 20 degrees downward due to it's own weight as soon as it is attached to the mount (figuratively). Obviously that's not acceptable. Construction is strong enough but not rigid enough. The question is how much more rigid you should make it?

Engine mounts are usually sized by the ultimate loads mentioned above.  An ultimate load may be significantly higher than normal operating load.  e.g. a 747-400 engine weighs ~10,000 lbf, but may experience, say, 6g during a very hard landing, or 10g during fan blade out, so the vertical load is now 100,000 lbf. Usually a mount that is strong enough to take the ultimate load will end up being stiff enough anyway.  But to answer your question, I think a few degrees / few inches would okay.  Since it will be a known displacement, the aero lines can be compensated for this.


text:
Were cargo pods ever fitted to the original Cessna Caravan?
Cargo pods are available on the Grand Caravan (C208B and EX), as shown here:

Image source
I'm trying to determine if cargo pods are (were?) fitted to the original (non-Grand) Caravan, either by the factory or a third party.  An internet search, including the Cessna website, did not turn up any examples.  However, I'm looking for a more definitive answer.

Yes, they have.  I have flown one with them, here's a photo:
(From the Wikipedia page for "Kenmore Air")


text:
What is the definition of "Sideline" in reference to aircraft noise?
The FAA has measured external aircraft noise levels and published the results in the Advisory Circular:
AC 36-1H - Noise Levels for U.S. Certificated and Foreign Aircraft
In the appendices, noise levels are listed for Takeoff (TO), Sideline (SL) and Approach (AP).
I understand the concept of Takeoff and Approach, but what is "Sideline"?   It is not defined in the document, nor does it show up in a search of the  Code of Federal Regulations.

Your document mentions a 450m distance on page 3.  See also http://adg.stanford.edu/aa241/noise/far36.txt mentioning more detail under C36.9(c)

More on the noise measurement: Noise Certification Workshop and ICAO Doc 9501 Procedures for the Noise Certification of Aircraft

The definitions are specific.
(They are defined in FAR Part 36).
I'm writing also the Take-off and approach noise definitions just for your information.

Sideline noise: is defined and measured 1476 ft (450 m) from the runway centerline at a point where the noise level after liftoff is greatest.

Take-off noise: is defined as the noise measured at a distance of 21,325 ft (6500 m) from the start of the take-off roll,
  directly under the airplane.

Approach noise: is also defined and measured under the airplane when it is at a distance of 6562 ft (2000 m) from the runway threshold.

For each of these conditions the maximum noise level is a function of maximum takeoff gross weight, and for the take-off case the limits depend also on the number of engines.


text:
How quickly should a maneuver be started when ATC gives new heading?
This is going to be a no-brainer for a pilot, I am sure. I am not one, however, only an enthusiast.
Scenario is: I am flying under the directions of ATC, into a relatively busy Class-B airport and am given a change of heading by them.

Piper N1234A, fly heading 235 ...

The radio is full of communications, and I cannot seem to be able to squeeze in to confirm receipt of heading change. I assume I would start the standard-rate turn immediately, and acknowledge as soon as possible, even if I've already completed the course change?

ATC is not supposed to assume you received any instructions without hearing a readback. The communications in busy airspace move quickly so incomplete instructions are common, but if you can't squeeze in a readback ATC will usually issue the instruction again

SMSvonderTann: sorry, but your edit changed my question from what I wanted to ask to something a bit different. The question isn't about an incomplete instruction from ATC. I stipulate the instruction was received in its entirety, just that the pilot is unable to acknowledge receipt. I wanted to ensure that the pilot is supposed to make the change immediately, and not wait until able to respond with an acknowledgment. Like I said, this is a no-brainer, but I wanted to know I understood the procedures correctly.

If other aircraft are interrupting between the giving of an instruction and its acknowledgement that's a massive violation of radio procedures by them, isn't it? Does that happen significantly often?

You are correct, you should turn to the assigned heading immediately unless you aren't sure of the instruction (was that 100 assignment a heading or a speed?).
When ATC gives you a change, it is based on a continuously changing environment and they want you comply right away, as long as it was clear. Usually, doing the wrong thing is worse than doing nothing at all.

What if the controller said: "turn right  heading 235, climb and maintain...." because of obstacles?  So you've turned but you are flying into a sector where you are now below the MVA

Isnt that the pilot's ultimate responsibility to maintain safe flight? Doesnt he always able to say 'unable' and wait for further instruction?

@rbp Then you are in a pickle, because where are the obstacles?  Straight ahead?  After you turn, but you are okay if you start to climb?  This is where your situation awareness becomes even more valuable than normal.  As you know, you have options, even up to declaring an emergency so that everyone else shuts up if it is needed.

@vasin1987 Yes, but what if going straight isn't safe?  Maybe the instructions were given to prevent an unsafe situation from developing (pretty common).  The controller continues to monitor everyone though, and if you don't turn when they expected you to, they should get back to you before it becomes a major problem.

Yeah typically the instruction will come through well before it becomes urgent in order to give time to repeat it if misheard, and react regardless. If it's urgent, you can probably expect an "expedite" to accompany the instruction.

the point i'm trying to make is that if you don't hear the entire instruction and repeat it back to him, all sorts of bad things can happen. if you do one part of the instruction but not the rest, then the controller is going to be more confused than if you did nothing at all.

@rbp I got your point, and I agree that if you don't understand an instruction (regardless of whether it is partial or a complete misunderstanding) then all sorts of bad things can happen....  This is very situation dependent, and doing nothing at all may even be the worst course of action.

Your are correct, but I'll offer a different reason than Lnafziger.

Aviate
Navigate
Communicate

Those are your priorities when flying.  It is more important that you fly the plane first than it is to answer, in terms of prioritizing your actions.
In class B, you are most likely in radar contact with that controller.  Your change in course will become apparent to the controller, and your eventual reply, when you can get it in, will confirm that you have correctly heard/read back the heading he gave you ... or that you have not!
Why it is necessary for flight safety to reply:
"Cougar 355, fly 030, maintain 4000."
You turn towards 300 (because you made a mistake) and you finally get in a radio Call
"Cougar 355, Roger, fly 300, maintain 4000"
The controller is now alerted that you went the wrong way, and he'll issue supplementary instructions (and also check to see if you are about to fly into someone else he has on the scope) ...


text:
What makes the perfect landing in a tail-dragger?
What is the 'perfect landing' in a tail-dragger? Do you try to float down to a main-gear landing at minimal descent speed, or do you attempt to float to the point where your tail will either start to come down, or does come down? In other words, is a two-point touchdown or a three-point touchdown more 'perfect.'?

I believe it differs from plane to plane.

Good piloting, good weather, and good luck.

They both have their uses.
A wheel landing (landing on the mains, keeping the tail in the air) gives you better rudder authority on the ground, which is useful in a crosswind or during touch-and-gos. However, there is a point where as your airspeed slows, your rudder authority falls off quickly. This can be dangerous in a crosswind for obvious reasons. Most pilots avoid this condition by keeping the tail up for as long as they can, then quickly planting it on the ground when it begins to fall. The rudder is kept up in the airstream for as long as possible, and then you quickly transfer your turning control from the rudder to the tailwheel.
A three-point landing is useful for getting on the ground and stopping quickly, because the additional wheel provides more friction. It also avoids the situation in the previous paragraph, because you land with the tailwheel down and have full turning authority the entire time.
So in general, there is no preferred landing style in a tailwheel airplane. This may not be true for specific models of aircraft, however.

You can make a perfect "wheelie" landing, depending on the wind and landing runway direction.
In a crosswind, it is safer to land on the main gear with the one windward wheel (wing low), or both main wheels, thus permitting better rudder control until the tail wheel makes ground contact as speed slows. In a crosswind the landing phase is done with a combo of wing low and/or crabbed into the wind.
Wind and aircraft load conditions dictate if you can manage a perfect 3 pointer called a "full stall landing"..the aim is to hold it off until the aircraft stalls an inch or so above terrain. By the way, an aircraft can fly in ground effect BELOW its stall speed.

Welcome to Aviation.SE! Your answer looks fine, but please consider improving the terminology (X wind -> crosswind, combo, a/c).


text:
Who is responsible for avoiding collisions on the ground; the pilot or the air traffic controller?
I may have some false assumptions here, so correct if needed. It is said that while ATC sounds like they are "in charge" of the airspace surrounding a major airport, control and responsibility for any given airliner is (still) in the hands of the Pilot-In-Command (PIC).
What this means is that if an airliner is given instructions to do something by ATC, and they are unable (or unwilling) to follow those instructions, they are able to tell ATC they are unable and ATC has to work it out, with all of the ramifications that implies. If the ATC controller wishes, they require the crew to contact ATC by other means (the dreaded phone call, I suppose) to explain, but the fact of the matter is, the passengers are ultimatley depending on the crew to keep them safe.
Now, let's take an airliner, at the gate, readying itself for a flight. They receive a pushback and are ready to taxi. They contact ATC Ground for instructions. Ground gives them taxi instructions. Who is responsible for the safety of the aircraft at that point?
Why do I ask this, when it should be obvious, the PIC. However, visibility out of the aircraft is limited, especially in some of the larger craft. As far as I know, there is no "check the mirrors" or "objects in the rear view window may be larger than they appear." The PIC simply CANNOT see behind the aircraft, and so any ground vehicles, personnel, or other aircraft (small or large) could cause an accident, which would be out of the control of the PIC.

It depends. In the maneuvering area, which encompasses runways and taxiways, aircraft (and all other vehicles) must obtain an ATC clearance to operate. On other areas of the airfield, such as the aprons ("ramps" for the American audience), ATC does not control traffic, but can still issue advice.

please don't answer in a comment...

At all times, whether in the air or on the ground, whether at the gate or taxiing, the pilot-in-command (PIC) has final and ultimate responsibility for the safe operation of the aircraft. Per ICAO Annex 2 (with similar statements/definitions by individual civil authorities):

The pilot-in-command of an aircraft shall, whether manipulating the controls or not, be responsible for the operation of the aircraft in accordance with the rules of the air, except that the pilot-in-command may depart from these rules in circumstances that render such departure absolutely necessary in the interests of safety.

As you stated, the pilot is allowed to deviate from any ATC instruction or regulation to the extent necessary to ensure the safety of the crew, passengers and property. If necessary, the PIC may enlist additional resources, such as a ground crew, to deal with issues like not being able to see behind the airplane. For airline operations, this is usually spelled out by the airline's operations procedures, which the PIC effectively "approves" (as the ultimate authority for the aircraft's operation) and carries out.
Air traffic controllers have what you might call "jurisdiction" over certain parcels of airspace and airports. The gates and the area immediately surrounding them are usually not under the jurisdiction of the control tower. They are instead managed by the airport authority. At large airports, the airport may operate a "ramp control" system with its own (smaller) control tower and radio frequencies. Arriving and departing aircraft coordinate with ramp control to get into and out of the gates safely. Ground crews will assist the pilot-in-command with parking and pushback operations, getting the aircraft to a point where the PIC can taxi the aircraft to leave the ramp area and enter the taxiway system in accordance with ATC taxi instructions.
Once on the taxiways, and from there to the runway and into the air, the aircraft is under the jurisdiction of the regular air traffic controllers. The controllers can divide up this area between different positions, usually a "ground controller," a "tower" or "local controller," and one or more approach/departure radar controllers.

At airports, everyone shares in the responsibility of safety. While the PIC ultimately has the responsibility of the safety of their aircraft, they cannot see and know everything from the cockpit. Each person is responsible for what they can see and what they have control of.
As explained by dvnrrs, the ground controllers (or ramp controllers at large airports) give clearance for pushback. If they can't look outside and see their area of control, they can use a computer screen that shows positions of aircraft. So the controllers are responsible for avoiding aircraft and vehicles which they can see, and the ground crew is responsible for avoiding anything that they can see. As you said, the pilots have very limited visibility for pushback, which is why the pushback tractor driver is there. There are usually additional ground crew that are responsible for ensuring that the wing tips clear any obstacles as well.
When the ground controller gives taxi instructions, again they are responsible for giving instructions that will avoid other aircraft they can see. The pilots are responsible for avoiding any obstacles they can see. In cases where the pilots don't have full visibility, such as wing tips, more care is required. ATC must ensure that the taxi instructions include only taxiways that are wide enough for the aircraft (some have width restrictions). The pilots must follow the taxiway correctly. Ground crew are responsible for parking aircraft so that they are well clear of the taxiways.


text:
How are taxi to and hold instructions given on an airport without taxiways to the runway end?
In a smaller airport which still handles large commercial aircraft (i.e. Princess Juliana Int. Airport (TNCM), Robert L. Bradshaw Int. Airport (TKPK), etc.), what are the taxi instructions given? I don't want to just assume that an airliner would be given a taxi and hold short, but that is what I would expect.
Here is a diagram of Bradshaw Airport,

Copyright, Acronautic
Let's say our commercial airliner is taking off from Runway 07. They get a Taxi To and Hold Short instruction preparatory to Cleared To Takeoff. Do they taxi to the end of ramp A and hold short? or do they go all the way to the turn around at the end of 07?
If it's the end of A, what instruction allows then to enter and use the runway as a taxiway?

A is a taxiway, not the ramp. It will have stop bars and signs at the end. Here, the double solid lines are on the taxiway side and must not be crossed without clearance.
If the instruction is hold short, you hold at the end of Alpha.
NB.  An active runway is never a taxiway.  The clearances and instructions are for runways, even when backtracking.
The initial clearance will likely be:

Taxi via Alpha, hold short runway 07.

Followed by

Line up runway 07 via backtrack and wait.

Then finally:

cleared for take-off runway 07

The initial clearance might combine the first 2.

Taxi via alpha, line up runway 07 via backtrack and wait

Note that the runway designator is always the departure runway so enter 25 and backtrack would not be used.

@CGCampbell -- Nota Bene -- it's not a pilot thing, just a writing thing :)

@CGCampbell NB is Latin, nothing to do with flying :-) https://en.m.wikipedia.org/wiki/Nota_bene

Backtrack is used by ICAO and Backtaxi is used by FAA, they mean the same (to travel on the runway in use in the oposite direction). Beware for in aviation the term backtrack has an implied clearance for 180º turn.
i.e.
An airfield with a single twy access to the rwy at midfield. If a landing a/c has roled past midfield, he has missed his exit twy. If ATC clears you to "vacate rwy backtrack approved", then you are cleared for 180º turn and taxi back on the rwy until you reach exiting twy.

If they're given a "hold short" instruction, then they don't enter the runway.  That's sacrosanct, since it's what protects the runway from an incursion if an aircraft will soon be using the runway to land or take off.
The instruction to enter the runway but not take off is "line up and wait," and to go back the length of Runway 7 and turn around is to "back taxi" (FAA term) or "backtrack" (ICAO term, same meaning) on the runway.
So let's say that an inbound aircraft has landed, and is past (northeast of) taxiway A but is still on the runway.  The aircraft ready to depart can be cleared onto runway 7 to back taxi (or "backtrack"), line up and wait -- but the tower wouldn't issue a takeoff clearance until the entire runway is clear.  But this clearance gets the departing aircraft moving toward the position he wants to be in, and by the time the back taxi is complete, the runway will probably be clear, so a takeoff clearance can be issued at that point.

Is back taxi a recognised phrase?  I've only ever read it and heard it as back track.

In the USA, I've only heard it as back taxi.

The PCG has back-taxi but not backtrack. https://www.faa.gov/air_traffic/publications/media/PCG_4-03-14.pdf#19

@DougMcClean I've obviously spent too much time on various SE sites, I read PCG as Programming Code Golf...


text:
Is a flying wing optimal for high altitude craft?
One of the biggest problems with flying wings is their sheer thickness, which creates excessive drag.
However, since high altitude craft need bigger (and thus thicker) wings anyway, and since weight us a bigger issue with these larger wings, and is addressed with the flying wing, would a flying wing not be the best option for accommodating the required payload volume for minimum surface area and weight extreme altitudes?
Yet high altitude aircraft up till now have used the tube and wing configuration. Why?

@ymb1 above airliner and bizjet height.

For maximum altitude, the primary distinction to be made is whether the airplane flies at subsonic or supersonic speed.
Subsonic speed
There are several factors for maximum altitude, but the maximum altitude of specially developed high altitude airplanes is determined by the coffin corner which in turn depends on the product of lift coefficient and Mach number squared. With a given $c_L\cdot M^2$ of about 0.4, which is as good as it gets, now altitude only depends on wing loading which has to be as low as possible for the best altitude. Note that the best subsonic performances were reached with electric propulsion because combustion engines will not work anymore with the low partial pressure of oxygen at altitude.
A high $c_L\cdot M^2$ can best be achieved with generous rear loading on the airfoil. This will upset the longitudinal stability of flying wings - using rear loading at the center will require generous downforce at the tips, and it is the overall $c_L$ that has to be counted for $c_L\cdot M^2$. Reflex airfoils are poor in that respect and do not come close to the value of 0.4 for $c_L\cdot M^2$ which is easily possible with rear loading.
That the altitude record holder is a flying wing shows that low wing loading is the most important feature for high altitude, but the Helios had neither crew nor a serious payload, so its practical usability was very limited. Add to that the fact that the structure was too fragile to survive even moderate gusts and it becomes obvious that a super lightweight span loader is not a practical design.
Supersonic speed
High means fast, and fast means draggy. As can be seen from the envelope of successful designs, they need to fly in a small range of dynamic pressure and have to fly faster to climb higher. Now thermal peak loads will limit what is possible and electric propulsion is out of the question. As a rough estimate for the possible drag at supersonic speed, Dietrich Küchemann once gave this approximation:
$$\left(\frac{L}{D}\right)_{max} = \frac{4\cdot(M+3)}{M}$$ which can be improved for waverider configurations to:
$$\left(\frac{L}{D}\right)_{max} = \frac{6\cdot(M+2)}{M}$$
Regardless which version you choose, both show that L/D suffers with increased flight Mach number $M$. At Mach 5 your best hope for L/D would be 8, only bit more than what Concorde reached at Mach 2. Partial oxygen pressure is of no concern since recompression at the intake will raise the pressure sufficiently - now flow speed and gas temperature in the combustion chamber will set limits to what is possible. The high level of thrust also means that the engine will determine the configuration. Sustained flight at more than Mach 5 has so far only been possible with rockets.
This means your optimum configuration is a slender Delta wing with a lot of internal volume for the hydrogen fuel required by the scramjet or it is a cylindrical pressure vessel with fins.


text:
What is the difference between CANPA and CDFA?
What is the difference between Constant Angle Non-Precision Approach (CANPA) and continuous descent final approach (CDFA)?

CANPA and CDFA are two identical terms.  CANPA was originally used, and it was replaced with CDFA per ICAO standards.


text:
Why do suborbital planes feature H-tail and/or large wingtips?
Spaceplanes that are suborbital are mostly supersonic and feature H-tail or rather large wingtips. This looks to be similar to a H-tail configuration but I'm unsure abut how it works, which is why I say large wing tips. They focus on a delta wing and elevon for the pitch and roll and yaw seems to be controlled using this.
For example look at the following spaceplanes.
References:
1. https://www.virgingalactic.com/articles/VSS-Unity-First-Powered-Flight/
2. https://www.sncorp.com/what-we-do/dream-chaser-space-vehicle/
3. https://www.flyfighterjet.com/xcor-lynx-space-flight

Most spaceplanes are aerodynamically just hypersonic airplanes. The tailless delta wing with directional stabilising fins on the tips is an optimal solution, especially if you do not want a fin on the fuselage. Directional stability can be elusive and highly non-linear, so types designed before the days of high-speed digital control systems often resorted to extra-large surfaces.
During re-entry a spaceplane cannot nosedive or it would overheat and melt or tear itself to bits. It has to kind of pancake down on its underside, keeping just enough forward speed to maintain aerodynamic control (An orbital craft needs hi-tech heat insulation even for this but for suborbital craft it is unlikely to be needed). The safe angle for this manoeuvre is really quite small with little room for error, just a few degrees either way. It was an acceptable risk for the Space Shuttle but may not be for commercial passenger flights.
SpaceShipOne and Two are a unique solution to the problem of safe re-entry. The tail configuration is known as the outboard tail or outboard horizontal stabilizer (OHS). It has been studied from time to time but never really flown (a German research prototype was built in WWII but it is unclear whether it ever flew). It was adopted for the SpaceShip series for the obvious reason that it gets the stabilizer out of the way of the rocket exhaust. It also eased the mechanical solution to their other big aerodynamic innovation, the variable-geometry "weathercock" tail. By swinging the tail up for re-entry, it stabilises the spaceplane as it pancakes back down, hugely increasing the safe zone and making re-entry almost trivially safe.
Passengers returning from actual orbit present a far greater challenge, as yet unsolved.

The massive winglets on a very slender delta wing are needed for directional stability and for a successful landing as a glider. While a central fin also would provide directional stability, it would produce higher sideslip-induced rolling due to its high location on the fuselage. Next, the rear fuselage is mainly a shell around the rocket motor and would need to be heavier to tolerate the loads from a massive tail. By shifting the vertical tails to the wingtip, they become more effective from their more rearward location.
But more important for the wingtip location of the fins is the L/D which would be too low without them for flaring during landing, especially in case of the Dreamchaser and the European Hermes re-entry vehicle project. Without the improvement in L/D, both would lose too much kinetic energy during the flare to cut down their sink speed before they stall.

Dreamchaser isn't intended to be suborbital. Don't know about your 3rd picture, but the Spaceship 1 & 2 were designed by the same person/company, so it's not surprising they use the same design elements.
The designs of Dreamchaser vs Spaceship N address two different problems.  An orbital vehicle has to decelerate from ~17,000 mph, while a suborbital vehicle on a ballistic trajectory (simplistically straight up and straight down) starts from zero speed at its high point, and needs to keep from gaining too much speed.  So if I'm not mistaken, a main function of the H-tail is to allow the entire vehicle to act as a drag device.  That wouldn't be practical for an orbital reentry vehicle due to heating & aerodynamic forces.

Dream Chaser worries about gaining too much speed too, especially during re-entry.  Both it and Space Ship 2 want to stably slow down from space to atmosphere and glide home.  The third plane is concept only, it's company went out of business.

In other words, after deorbit burn, Dream Chaser, now suborbital, but with much more potential and kinetic energy, must slow down and glide as well.  So needs heat shield, Space Ship 2, not as much.

@Robert DiGiovanni:  As I said, suborbital flights start from essentially zero speed at the top of their arc, and want to keep from gaining speed (think parachute).  Any orbital reentry vehicle starts from orbital speed (otherwise it wouldn't be in orbit, of course) and slows down.  The problem there is to manage the slowing in a controlled way.

Here's where it gets good. An object in orbit starts with 0 vertical speed as well. It's all potential energy.  It does have horizontal speed, and so does sub-orb (think Redstone). The task of returning to around 200 knot glide through the air is the same, why separate them?  There for Dream Chaser is qualified for sub-orb flight.  Imagine how much smaller the Space Shuttle's fuel tanks would be if it were sub orb as well.

When Spaceship 2 feathers in vacuum, it will accelerate quite a bit before entering denser atmosphere.  Not enough for significant heating, so I agree the strategy is more "parachute".  Both want to be stable, hence the heartfelt efforts at weight low, drag high.

Going straight down requires G forces to pull out.  I would hang on to some horizontal V and try to stretch my vertical descent over time.  Compare Mercury Gs to Space Shuttle!

@Robert DiGiovanni: First, speed is not a vector quantity.  Second, per Wikipedia https://en.wikipedia.org/wiki/SpaceShipOne Spaceship 1's maximum speed is about 2000 mph (900 m/s) vs the 17K mph (7800 m/s) of orbital velocity.  So obviously the energy you need to dissipate in returning from orbit is much greater, as are the structural forces & heating.  WRT stretching the slowing over time, of course.  I'm just looking at the worst case, which is going straight down until you need to pull out.

We humans measure altitude in feet and distance in miles.  An object falling at 1200 mph (20 miles per minute) would impact the earth in 60 seconds from 100,000 feet.  Good thought conceptually, but straight down is not an option from space.  Certainly wishing Spaceship 2 the best though, they have worked very hard to get it flying!

@ Robert DiGiovanni: Humans - at least some of us - may use feet and miles.  Wikipedia uses meters &c, and I'm too lazy to do the conversion.  WRT falling straight down, SS1 would start from an altitude of 62 miles (!327K ft) or greater (that being the definition of "space" for the X-prize), and zero vertical speed. so it would take rather more than 60 seconds to impact the Earth, even if not slowed by air friction.  Which slowing - coming full circle - is the purpose of the H-tail arrangement.

Depends what you like, the Lancaster has an H tail, the B 29 straight vertical.  Not too happy with SS2 Gs.  Read how Apollo reduced theirs by lifting (gliding) the capsule instead of ballistic trajectory.  Thanks.

At extreme speed, the more symmetry you have, the better your chances are of staying straight.  This is especially of concern at very high altitudes, where
aerodynamic forces (indicated airspeed) are small.
X15 is good example of this.  Also, H type tail helps
keep control surfaces away from the rocket nozzle.
Shuttle type vehicles also emphasize roll and pitch stability in re-entry.  Very interesting to note the humble capsule has 360 degrees of roll stability (there for also pitch). The Soviets liked the ball, with the weight set a little low, for the same reason.
Space ship 2 has the (shuttle cock) feathered configuration.  Dream Chaser (and the Air Force)
has strong dihedral. These just want to come in upright and land safely.


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Is the National Aviation Authority the same as the Civil Aviation Authority?
Are the NAA (National aviation authority) and the CAA (Civil aviation authority) the same organisation? According Wikipedia it looks like they are the same organisation.

Welcome to the site @Akiyo. What country are you asking about?

Which country do you mean?

Hello Dan, I meant in general, if there is any difference between does two? Or is it exactly the same type of organisation just called differently in some countries?

The terms National Aviation Authority and Civil Aviation Authority are indeed two generic terms to describe the same thing - the government organisation responsible for managing non-military aviation within a country.
It's worth noting that the specifics of how the organisation works and what it regulates is down to each country, so the terms are broad and generic. For example, Iceland doesn't have any kind of specific CAA - rather, those roles are performed by the Icelandic Transport Authority.
In addition, it wouldn't really be right to refer to a countries authority as the National Aviation Authority or the Civil Aviation Authority (Unless that's what they've called themselves).
For example, the FAA is an example of a National Aviation Authority, it isn't known as the National Aviation Authority. The UK's Civil Aviation Authority is the Civil Aviation Authority in the UK and an example of a National Aviation Authority


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Does the Cessna POH state the fuel consumption in Imperial or US Gallons?
I'm planning a trip in a Cessna 182T and was calculating fuel requirements and started wondering. I have always assumed that fuel consumption is in US Gallons (or 3.785 litres) but I can't find a section in the Pilot's Operating Handbook (POH) that really confirms this. The fuel tank capacity is expressed in USG so I reckon it's close to assume that this implies that GPH is US gallons per hour.
There is a Imp. Gallon to Liter and Imp Gallon to US Gallon conversion table in the POH, when do we need Imp. Gallons?
Any comments, did I miss something?

The plane was certified with US Gallons. Use those for fuel consumption.
The conversion tables are there in case your FBO's fuel pump is calibrated in L or Imp Gal.

Okay... I came about 1 U.S. Inch from posting a long bewildered comment trying to understand what the airplane's fuel pump has to do with this, and then, I realized you are talking about the FBO's fuel sales pump.

@MortensenAviation, thank you for specifying that it was a U.S. inch, otherwise, we would have had to have another discussion about that. :)

I am currently flying cessna 152(ii) and I have my POH which is from the year of 1979. The fuel per consumption and other performance data are given in the performance section of the POH at section 5. The arrangement of data and other information are similar for all the POH. So you will get it in the section 5 probably. There are some tables which dictates information regarding cruise range, endurance, cruise performance. In the cruise performance chart you will get the consumption of fuel in accordance with temperature and RRP and if you have manifold pressure system you will have it on this chart hopefully. And for the calculation of fuel you will depend on the the calibration of the gauge you have in the cockpit. I think the on the chart of POH the fuel consumption is given in US Gallon.
Hopefully this will help you.


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Is autorotation possible in a tandem rotored helicopter?
I just wonder, whether a synchronized autorotation is possible in case of turbine failure (one or both gas turbine engines). All Gearboxes obviously must turn not to desynchronize -> lethal

I'm a little confused, why would you need to auto-rotate if only one engine failed in a twin engine helicopter? Are you assuming that the freewheeling unit doesn't disconnect? Or are you unaware of the operation of the freewheeling unit in helicopters?

Not just possible, in the Marines it's how we introduced newbie infantry to the wonders of flying helicopters. :)

On the Chinook, the sprag clutches that allow the drive system to freewheel when an engine fails are between each engine's step-down transmission and the "combining transmission" that receives torque from each engine and sends it to the front and rear rotor transmissions.
This means that the entire drive line between the rotors always remains engaged and in sync regardless of whether any power is being supplied. If one engine fails, it's simply disconnected from the drive system by its sprag clutch with the remaining engine doing the work, like any helicopter.  And if both engines are shut down, same deal; both engines are disconnected by their sprag clutches and the still interconnected rotor system will autorotate with the correct blade intermesh maintained.
So the Chinook can loose one engine and continue flying (more or less), or lose both both engines and glide to land like any multi-engine helicopter.  If you loose one of the gearboxes or drive shafts in the interconnected system however, now you have an unpleasant situation.

Yes-not being able to autorotate means no sale
I used to watch the CH-46 doing practice autorotations at an outlying fiend when I was in Norfolk in the 1980's.   Given that the CH-46 (and its larger cousin the CH-47) are designed and built for the harsh military operational environment, where one could expect all manner of things to go wrong due to enemy fire, the inability to autorotate would mean that the military specification for that was not met and thus Boeing could not have sold them to the Army and the Navy.
The fundamental design principal at work is, in plain language:
You need for those in the damaged helicopter, or when the engines quit, to have a chance to walk away from it.
Both helicopters' designs included sprag clutches or a similar free wheeling
unit that would disengage from the rotors if engine drive was lost, allowing the pilots (providing they are within the proper performance envelope) a shot at an autorotation. (Check the H-V diagram for specifics).  If only one engine is lost, the extent that one can fly with a single engine will depend on gross weight and environmental conditions / operating environment.
Now that you mention it, I don't think that there is a single helicopter, absent some corner cases for unusual experimental models, that can achieve certification without demonstrating autorotation capability. Relevant civil requirements are 14 CFR 27.71/27.691 (normal category) and 14 CFR 29.691 (transport category). Tip of the cap to @UnrecognizedFallingObject for confirming the certs.

For civilian whirlybirds, the requirement is in 14 CFR 27.71/27.691 (normal category, albeit a bit obliquely worded) and 29.691 (transport category)

@UnrecognizedFallingObject thank you


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Can an airliner be landed with only the auto pilot or remotely?
In this question: How autonomous are commercial passenger airliners? explains how automated the auto-pilot system can be. Could a pilot or more work the controls of the auto pilot that does not have auto-land to land a plane? How would this be done?
Some of the cars have the ability to be turned off remotely. In an emergency situation could any aspect of the plane be de or activated remotely?

Airplanes have been able to land on autopilots for a long time. E.g. the Airbus A320 flew for the first time in 1987 and it can auto-land using the instrument landing system ILS.
Even the Concorde could land on autopilot.
Honestly just google autoland or search on youtube and you'll find tens of thousands of results and videos.
There have also been airliners that were turned into radio controlled aircraft for emergency crash testing.

An increasing number of big commercial aircraft do have an autoland system. It requires a minimum of Cat III ILS equipment on the ground, and current systems don't respond to wind shear very effectively. It also certainly can't be activated remotely, the pilot has to set it up.

What about landing it using auto-pilot?

@Muze On planes that have autoland, it's a feature of the autopilot.

I included that thanks

As a sidebar comment.... We used to have CAT II capable 727’s and CAT III capable 727’s. It was a bit of a mixed bag. It was fairly common for a flight crew to write “SAT CAT III w/ rollout” on planes that were only CAT II capable. We’d always scratch our head and info note it. The difference is really about the redundancy of the auto land system and not the capabilities of any one autopilot. They were basically shooting CAT III’s with zero redundancy and didn’t know it.

@Muze Are you talking about manually tweaking the descent rate, course, etc. in the autopilot to land in a plane without autoland? No, that's not possible. If nothing else, the autopilot wouldn't flare properly, smashing the plane into the ground and breaking the landing gear (and probably a lot of other stuff as well). And that's assuming the autopilot isn't tied into the GPWS (a lot of them are), which would cause it to either pull up or switch to manual hundreds of feet off the ground.

@HiddenWindshield Actually, I’ve never seen an autopilot tied to the GPWS. GPWS has absolutely no override capability whatsoever with, perhaps, exception of hierarchical audible alerts. In other words, GPWS audible alerts override TCAS audible alerts (dodge the mountain then worry about the plane in front of you), but they cannot take over the aircraft at all. Otherwise you have an MCAS-type situation.

@Frank I've heard both ways. I don't have any experience whatsoever in the autopilots in big jets, so I bow to your experience.

@HiddenWindshield It’s all good!


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What is the minimum separation for aircraft operating on or intersecting the same runway?
How capturing of this photo was ever possible:

(photo courtesy of jetphotos.com)
Shouldn't there be a bigger time / distance separation of three aircrafts using, operating or intersecting the same runway?
Shouldn't pictured situation be considered as a bit dangerous in terms of ground operations?

This is not a picture of a landing strip, it is a picture of a set of taxiways. These planes are simply taxiing (i.e. driving around on the ground at low speed, on their way between the runway and the gate)

@J.Hougaard Thanks for explaining me, what taxing is! :> I was aware of this, but it is always so nice if someone cares enough to explain words used.

Same location (intersection of taxiways N1 and N2), more aircraft. Runway 09-27 is on the left side. Airport diagram page 43.

If you see similar pictures in future, look at the color of the painted lines at the edge of the tarmac. Runway lines are white, taxiway lines are yellow. As you can see, the ones in your picture are all yellow, so the aircraft are on a taxiway, not a runway.

As both aircraft are still on a taxiway, turning into two different intersections it's absolutely normal. Each intersection has a so called "holding point" where all aircraft must hold until a clearance to enter the runway is given.
In this particular situation the tower controller will ensure that only one aircraft enters the runway and waits until departure separation minima are given before clearing the second aircraft for takeoff.
In this way maximum efficiency is reached by using different intersections as the following aircraft can line up (and hold on the runway; only after receiving a clearance to do so of course) immediately behind the first aircraft.


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How is a carpet plot for aircraft sizing constructed?
Generally, Carpet Plots are constructed to find out an optimal design which will satisfy all the performance needs and is least in weight & cost.
I want to know how to construct such a carpet plot.
I have seen lines of constant weight in many carpet plots with T/W and W/S in the Y and X-axis respectively. But, I don't know how they constructed that constant weight line.
If there are some good references for constructing these types of sizing plots, please let me know.

Any book about general airplane design describes in a clear way carpet plots and how to plot them. You can find for example a list of books in this answer of mine

You might check out this package on the Matlab file exchange.
Set up a matrix or a grid of T/W and W/S.  Then do your calculations and calculate weight, operating cost, or whatever metric you want for each T/W, W/S in the matrix.
Then, use a contour plotting routine to generate isolines (isoline means a line of constant value).  Basically, the contour routine will interpolate from the values in your grid to find the location of your isoline.
Using contour plots like this is a very powerful technique to effectively 'invert' functions that are otherwise not invertible.  This is a pretty direct application of the implicit function theorem f(x,y)=0.
The carpet plot toolkit linked above has some routines to help transform 'normal' contour lines onto a carpet plot.  I believe the blue contours and also the red and green constraints depicted in the example were evaluated with a contour algorithm.


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How much energy/prop efficiency does the e-volo copter sacrifice by having a smaller propeller?
It seems like on an electric aircraft, it would be very important to have a high energy efficiency. Wouldn't the e-volo copter be much less efficient due to the small radius of the propellers when compared to a traditional helicopter?

When a helicopter is hovering ideally it should take no horsepower or energy to maintain that state. The larger the rotor the closer you can approach that. Maybe the worst case is to use a rocket, which is probably the least efficient way to hover.

What counts is the mass of air which is available for lift/thrust creation. Several smaller props would still offer about the same area for lift creation as a single rotor, so in this respect that design is not at a disadvantage. The smaller props will have to spin faster than a single rotor to have the same average dynamic pressure, and the lift distribution over the whole area covered by propellers will be less asymmetric at forward speed than it is over the disc of a single rotor.
What should reduce the efficiency, however, is the smaller Reynolds number of the blades. Even if the blade airfoil is carefully optimized for their small Reynolds number, I would expect that at least 10% more energy is needed for the same lift compared to a conventional helicopter. The smaller inertia of the blades, however, is a big advantage in control, because the smaller propellers can be spun up or down faster, avoiding the more complex rotor head of conventional helicopters. With a modern FCS the e-volo should be controllable by individually adjusting prop speed alone. The electric motors most likely are capable of short-term torque bursts which far exceed their continuous performance, so control responsiveness should be adequate.
The smaller moment of inertia of the propellers becomes a liability in an emergency, because the e-volo arrangement is less capable of an autorotation landing in case the energy supply fails. That is probably the reason why the e-volo carries a full aircraft parachute. On the other hand, many small engines and propellers certainly improve redundancy over conventional helicopters.
I also have to wonder about the mass of the massive framework which is used to mount the rotors. It is in the way of the propeller flow and should contribute a substantial fraction to the empty mass of the e-volo. I expect the designers use it to store the battery cells, but I could not find much about this on the website - which offers, however, a funny movie which nicely sums up the projected capabilities. Just don't get distracted while the e-volo waits for you in hover mode: The claimed flight time is currently only 20 minutes.
My verdict: It is less efficient than a comparable helicopter, but not by much. The two problems are the lower blade chord, which translates into more viscous friction, and the high mass and drag of the framework.


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Is the maximum power the Merlin 61 reciprocating engine occuring at its maximum RPM?
Looking at the stats breakdown on Wikipedia here for the Merlin 61 series reciprocating engines used in Spitfire planes, I noticed that maximum horsepower is given at approximately 3000 RPM. But AirPages has what looks like a manual here that lists the maximum RPM as 3000.
Are they simply stating that the same thing: that torque starts to fall off at 3000 RPM? Or are they saying that the engine is just physically incapably of spinning faster than 3000 RPM (seems unlikely)?
In the case of the first one, what is the (approximate) redline for one of these engines?

Power is torque x RPM and goes up linearly with engine speed. And the limit speed of the Merlin was indeed 3000 RPM, which was quite fast for its time.

Power output of a reciprocating engine goes up with speed, and yes, maximum power is reached at maximum RPM. Considering the size and age of the Merlin 61 (27 liters displacement) it had a rather high maximum speed. Some contemporary engines ran even slower:

Daimler-Benz 601E: 2700 RPM for take-off, 2326 RPM continuous power
Daimler-Benz 605A: 2800 RPM for take-off, 2300 RPM continuous power
Allison V-1710-A: 2800 RPM
Klimov VK-107: 3200 RPM for take-off, 2800 RPM continuous power
Jumo 213A: 3250 RPM for take-off, 2900 RPM continuous power

Note that the considerably smaller GA engines still only allow a maximum speed of 2700 RPM. The smaller the engine becomes, the higher the maximum RPM will be. Model engines for RC racing easily top 50.000 RPM.
Age is also a factor. Modern engines run much faster, and the early rotary engines of WW I would run 1350 RPM, max. The radial engine of the Boeing Stearman which I once flew was limited at 1700 RPM, requiring me to throttle back when accelerating for a loop-the-loop so I would not overspeed the engine in the dive.

Maximum RPM and Red Line RPM are the same thing.
They can be exceeded but not without the chance of engine damage.

What is confusing to me is that the red line RPM would be the same as the RPM at which the maximum horsepower is produced. Compared to a car engine, for example, where the maximum horsepower may be produced at something like 3000 RPM, but the red line RPM would be something like 6000 RPM

I suppose that is because aircraft engines have to be more reliable than other types of engines.

@Habitablaba; You are confusing torque with power. Torque might peak at 3000 RPM, but power goes up until you hit max. RPM.